Combination hall effect position sensor and switch

ABSTRACT

A combination Hall effect position sensor and switch for sensing the position of a moveable object. The sensor has a magnet that is attachable to the moveable object. The magnet has a pair of ends and a central portion. A linear magnetic flux sensor is positioned about the central portion of the magnet. The linear magnetic flux sensor generates an electrical signal indicative of a specific position of the movable object. A switch type magnetic flux sensor is positioned about one of the ends of the magnet. The switch type magnetic flux sensor generates an electrical signal that is indicative of the movable object reaching a pre-determined location.

BACKGROUND

1. Technical Field

This invention relates, in general, to position sensors. Moreparticularly, this invention relates to a sensor that uses Hall effectdevices to generate signals indicating positional information.

2. Background Art

Position sensing is used to electronically monitor the position ormovement of a mechanical component. The position sensor produces anelectrical signal that varies as the position of the component inquestion varies. Electrical position sensors are a part of manyproducts. For example, position sensors allow the status of variousautomotive components to be monitored and controlled electronically.

A position sensor needs to be accurate, in that it must give anappropriate electrical signal based upon the position measured. Ifinaccurate, a position sensor may hinder the proper evaluation andcontrol of the position of the component being monitored.

Typically it is also described that a position sensor be adequatelyprecise in its measurement. However, the precision needed in measuring aposition will obviously vary depending upon the particular circumstancesof use. For some purposes only a rough indication of position isnecessary; for instance, an indication of whether a valve is mostly openor mostly closed. In other applications more precise indication ofposition may be needed.

A position sensor should also be sufficiently durable for theenvironment in which it is placed. For example, a position sensor usedon an automotive valve may experience almost constant movement while theautomobile is in operation. Such a position sensor should be constructedof mechanical and electrical components to allow the sensor to remainsufficiently accurate and precise during its projected lifetime, despiteconsiderable mechanical vibrations and thermal extremes and gradients.

In the past, position sensors were typically of the “contact” variety. Acontacting position sensor requires physical contact to produce theelectrical signal. Contacting position sensors typically consist ofpotentiometers to produce electrical signals that vary as a function ofthe component's position. Contacting position sensors are generallyaccurate and precise. Unfortunately, the wear due to contact duringmovement of contacting position sensors has limited their durability.Also, the friction resulting from the contact can degrade the operationof the component. Further, water intrusion into a potentiometric sensorcan disable the sensor.

One important advancement in sensor technology has been the developmentof non-contacting position sensors. A non-contacting position sensor(“NPS”) does not require physical contact between the signal generatorand the sensing element. Instead, an NPS utilizes magnets to generatemagnetic fields that vary as a function of position, and devices todetect varying magnetic fields to measure the position of the componentto be monitored. Often, a Hall effect device is used to produce anelectrical signal that is dependent upon the magnitude and polarity ofthe magnetic flux incident upon the device. The Hall effect device maybe physically attached to the component to be monitored and thus movesrelative to the stationary magnets as the component moves. Conversely,the Hall effect device may be stationary with the magnets affixed to thecomponent to be monitored. In either case, the position of the componentto be monitored can be determined by the electrical signal produced bythe Hall effect device.

The use of an NPS presents several distinct advantages over the use of acontacting position sensor. Because an NPS does not require physicalcontact between the signal generator and the sensing element, there isless physical wear during operation, resulting in greater durability ofthe sensor. The use of an NPS is also advantageous because the lack ofany physical contact between the items being monitored and the sensoritself results in reduced drag.

While the use of an NPS presents several advantages, there are alsoseveral disadvantages that must be overcome in order for an NPS to be asatisfactory position sensor for many applications. Magneticirregularities or imperfections can compromise the precision andaccuracy of an NPS. The accuracy and precision of an NPS can also beaffected by the numerous mechanical vibrations and perturbations likelybe to experienced by the sensor. Because there is no physical contactbetween the item to be monitored and the sensor, it is possible for themto be knocked out of alignment by such vibrations and perturbations. Amisalignment can result in the measured magnetic field at any particularlocation not being what it would be in the original alignment. Becausethe measured magnetic field can be different than that when properlyaligned the perceived position can be inaccurate. Linearity of magneticfield strength and the resulting signal is also a concern.

In determining the position of the item being monitored, it is useful toknow when the sensor has reached or moved to a certain location. Once agiven position has been reached, a mechanism can provide feedbackindicating that the pre-determined position has been achieved.Typically, such a mechanism has taken the form of a separate contactswitch. Unfortunately, adding a separate switch complicates thepackaging of the position sensor, adds extra cost and increases theoverall size of the sensor.

There is a need for a compact, low cost position sensor that isintegrated into a single package and provides position and relatedinformation.

SUMMARY

It is a feature of the present invention to provide a combination halleffect position sensor and switch.

It is another feature of the present invention to provide a sensor thatgenerates signals for indicating the position of a movable object. Thesensor includes a magnet attachable to the moveable object. The magnethas a pair of ends and a central portion. A linear magnetic flux sensoris positioned near the central portion of the magnet and a switch-typemagnetic flux sensor is positioned about one of the ends. The linearmagnetic flux sensor generates an electrical signal indicative of aspecific position of the movable object. Further, the switch-typemagnetic flux sensor generates an electrical signal indicative of themovable object reaching a pre-determined position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of a combination Hall effect positionsensor and switch;

FIG. 2 illustrates a graph of mechanical position versus output signalsfor the sensor and switch of FIG. 1;

FIG. 3 illustrates a side view of the preferred embodiment of acombination Hall effect position sensor and switch;

FIG. 4 illustrates a graph of mechanical position versus magnetic fluxdensity for the magnet of FIG. 3;

FIG. 5 illustrates an alternative magnet design for the sensor andswitch of FIG. 3;

FIG. 6 illustrates a graph of mechanical position versus magnetic fluxdensity for the magnet of FIG. 5;

FIG. 7 illustrates an exploded view of the combination Hall effectposition sensor and switch of FIG. 3 packaged in a housing;

FIG. 8 illustrates a perspective assembled view of FIG. 7.

FIG. 9 illustrates a perspective view of the assembled sensor and switchof FIG. 8 mounted to a clutch pedal.

It is noted that the drawings of the invention are not to scale.

DETAILED DESCRIPTION

First Embodiment

Referring to FIG. 1, a combination Hall effect position sensor andswitch 100 is shown. Preferably the sensor and switch 100 has apermanent magnet 102 that is polarized such that it has a north end 104,a south end 106 and a central region or portion 108. Permanent magnet102 can be made from several different ferro-magnetic materials such as,but not limited to, ferrite or samarium cobalt or neodymium-iron-boron.Magnet 102 is attachable in a conventional manner to a movable object ormember 110 such as by adhesive or mechanical fastening means. Movableobject 110 can be a rotatable shaft, a reciprocating lever, a pedal orother movable member. As such, movable object 110 can be adapted to moveeither linearly, rotationally, or along an arcuate planar path. Sensorand switch 100 are configured to work with the linear, rotational orarcuate motion of the moveable object 110.

A switch type magnetic flux sensor, such as a conventional switch-typeHall effect device 112 is positioned adjacent or near the magnet northend 104. Another conventional switch-type magnetic flux sensor, such asa switch-type Hall effect device 116 is positioned adjacent or near themagnet south end 106. Switch-type Hall effect devices 112 and 116 arecommercially available as model HAL1000 from Micronas company of Zurich,Switzerland. Switch-type Hall effect devices 112 and 116 produce a stepoutput once the gauss level exceeds a certain level. For example, if themagnetic flux level sensed exceeds 300 gauss or 30 milli-tesla (mT),Hall effect devices 112 and 116 will switch output from 0 volts to 5volts. Accordingly, when Hall effect device 112 or 116 is located aboutmagnet 102 as shown in FIG. 1, the Hall effect devices will be turned onand have an output of 5 volts. However, if movable member 110 moves suchas to also move magnet 102 to the right Hall effect device 112 will nolonger be about the north end 104, and thus the output of Hall effectdevice 112 switches to 0 volts. Similarly, if movable object 110 movesto the left such that Hall effect device 116 is no longer about thesouth end 106 of magnet 102, then the output of Hall effect device 116switches to 0 volts.

A ratiometric or linear output type magnetic flux sensor, such as alinear type Hall effect device 114 is positioned adjacent or near themagnet central portion 108. Hall effect devices 112, 114 and 116 areseparated from magnet 102 by a gap or open space 118.

Linear type Hall effect device 114 is commercially available as modelHAL815 from Micronas company of Zurich, Switzerland. Linear type Halleffect device 114 produces a linearly changing output voltage dependingupon the polarity of the magnetic field sensed. For example, when thepolarity changes from North through the zero point to South, Hall effectdevice 114 will output a voltage that varies linearly from 0.50 volts to4.50 volts.

FIG. 2 shows a graph of mechanical position versus the output signalsfor the sensor and switch of FIG. 1. As stated previously, theelectrical output signal of switch Hall effect devices 112 and 114changes in a step function. Moreover, the electrical output signal oflinear Hall effect device 114 changes linearly.

Preferred Embodiment

FIG. 3 illustrates a side view of the second or preferred embodiment ofa combination Hall effect position sensor and switch 290. Sensor andswitch 290 has a magnet assembly 300 with a pair of pole pieces orplates including a first plate 301 and second plate 302. The first plate301 has a first end 551, a second end 552, and a middle 553. The secondplate 302 likewise has a first end 561, a second end 562, and a middle563. It is to be appreciated that the first plate 301 and second plate302 may be of any shape, and the reference to “ends” is used for purposeof demonstration, not to limit the scope of configurations possiblewithin the scope of the present invention.

The first magnet region 321 has a thin end 521 and an opposite thick end531 with a tapered portion therebetween. The first magnet region 321 isaffixed to the first plate 301 such that the thin end 521 is proximateto the middle 553 of the first plate 301, while the thick end 531 isproximate to the first end 551 of the first plate 301. The first magnet321 produces a varying magnetic flux field from the thin end to thethick end, as indicated by vectors 600 in FIG. 3. The polarity of themagnetic field generated by the first magnet region 321 is indicated bythe upward direction of the vectors 600. The polarity of the magneticfield generated by the first magnet 321 is denoted the first polarityand defined as positive. Likewise, the strength of the magnetic fluxfield is indicated by the length of the vectors. As can be seen in FIG.3, the magnetic flux field generated by the first magnet 321 decreasesin strength from the thick end 531 to the thin end 521. Like magnet 321,magnets 322, 323 and 324 are similarly designed as illustrated. Asrecognized by those having skill in the art, the third magnet region 323and the first magnet region 321 are described as linearly orsymmetrically adjacent, or simply adjacent. Likewise, the second magnetregion 322 and the fourth magnet region 324 are described as linearly orsymmetrically adjacent, or simply adjacent.

The four tapered magnets 321, 322, 323, and 324 can be formed of bondedferrite or other magnetic materials. A first gap 581 is shown separatingthe thin end 521 of the first magnet 321 from the thin end 523 of thethird magnet 323. A second gap 582 separates the thin end 522 of thesecond magnet 322 from the thin end 524 of the fourth magnet 324. Whilethe gaps 581 and 582 can be omitted without departing from the scope ofthe present invention, they serve important functions. In particular,the gaps 581 and 582 increase the consistency of the linearity of themagnetic field within the space or void 516 between the magnets attachedto plates 301 and 302. As a practical matter, the thin end of a magnetwill always have a finite thickness and generate a non-zero magneticfield. If the thin ends of two magnets having opposite polarities areimmediately adjacent, there will be a discontinuity of the combinedmagnetic field about the symmetry point 543. Gaps 581 and 582 allow fora consistent neutral zone, at around point 543 independent ofmagnetizing property variations, which aids linearity of sensor output.The gaps 581 and 582 can be created during the molding of the magnets.If the magnets are formed individually, the gaps 581 and 582 may beformed by appropriately positioning the individual magnets.Alternatively, magnetic material may be removed to create the gaps afterthe magnets have been formed.

The air gap 516 is formed between the magnet regions 321, 322, 323 and324. Preferably, the air gap or space or void 516 between the magnets321, 322, 323 and 324 is essentially diamond shaped, with the centralportion of the air gap 517 being larger than both ends 518 of the airgap 516. A linear magnetic flux sensor such as a Hall effect device 114is positioned within the air gap or void 516. A switch Hall effectdevice 112 is also located in air gap 576 between magnet regions 321 and322. The relative lateral movement between the Hall effect device 114and the magnets causes the position of the Hall effect device 114 withinthe air gap 516 to vary along plane or line 540. The magnetic fieldwithin the air gap 516 is the sum of the magnetic fields generated bythe first magnet 321, the second magnet region 322, the third magnet 323and the fourth magnet region 324.

The polarity and strength of the combined magnetic field varies alongthe axis or line 540. One end of line 540 is at about position 541 andthe other end is at about position 542. The magnetic field generated bythe first magnet 321 and the second magnet 322 is defined as positive.The magnetic field generated by the third magnet 323 and the fourthmagnet is defined as negative.

Magnet assembly 300 can be attached to a movable object that rotates ormoves linearly. Magnet assembly 300 can move to the left or right of theposition shown. The magnetic field detected by the Hall effect device114 as it moves along the line 540 will be large and positive at thefirst end 541 of the air gap and decrease substantially linearly as itapproaches the middle 543 of the air gap, at which point the magneticfield will be substantially zero. Magnet assembly 300 is preferablydesigned and constrained so as to not to move to the left.

Switch Hall effect device 112 is located at position 541 to start. Halleffect device 112 travels along the line 540 between position 543 andposition 544. At about position 541, switch Hall effect device 112 willbe in the presence of a flux field that is strong enough to keep itswitched on. As the magnets move to the right and Hall effect device 112relatively goes to position 544, the strength of the flux field rapidlyfalls off with distance from ends 531 and 532 of the magnet. This fluxchange is sensed by Hall device 112 and causes device 112 to switchoutput from a high state of 5 volts to a low state of 0 volts output.

Hall devices 112 and 114 would be connected to additional signalconditioning circuitry (not shown) that would amplify and condition theelectrical signals. It is noted that the switch Hall effect device 112could be configured to switch from 0 volts at position 541 to 5 volts atposition 544 if desired by modifying the signal conditioning circuitry.

Magnet assembly 300 is preferably designed and constrained so as to notmove to the left. This avoids any possible problems with Hall effectswitch 112 switching in a region of low magnetic flux such as atposition 543.

FIG. 4 illustrates a graph of mechanical position versus magnetic fluxdensity for magnet assembly 300. In FIG. 4, the x-axis denotes theposition of the Hall effect devices 112 and 114 along line 540 and they-axis illustrates the magnetic flux density detected. As can be seen,the magnetic flux density measured by the Hall effect device 114 atposition 543 is low and goes to high at position 541. The flux measuredby Hall device 114 has a low gradient or rate of change. The measuredmagnetic flux density is substantially linear between position 541 andposition 543, with the point of substantially zero magnetic flux densitybeing located at position 543. The magnetic flux density measured by theHall effect device 112 at position 541 is high and rapidly falls to zeroat position 544. The magnetic flux measured by Hall device 112 has ahigh gradient or rate of change, resulting in low variability in theswitch point position.

Third Embodiment

FIG. 5 illustrates a third embodiment that uses an alternative magnetassembly design. Magnet assembly 700 is similar to magnet assembly 300except that additional field shaping magnets 702, 703, 704 and 705 havebeen added. Magnet 702 adjoins end 531 of magnet 321. Magnet 703 adjoinsthe end 532 of magnet region 322. Magnet 704 is adjoins end 533 ofmagnet 323. Magnet 705 adjoins the end 534 of magnet 324. Field shapingmagnets 702, 703, 704 and 705 are polarized opposite to the polarizationof magnets 321, 322, 323 and 324. Compared to the magnet assembly 300 ofFIG. 3, field shaping magnets 702, 703, 704 and 705 cause the magneticflux field detected by switch Hall effect device 112 to have a largergradient with a change in position or to change more quickly as magnetassembly 700 is moved. This allows for more precise switch positions forswitch Hall device 112.

FIG. 6 shows a graph of mechanical position versus magnetic flux densityfor magnet assembly 700 and 300 as they move from position 541 to 544.As can be seen in FIG. 6, the flux density for magnet assembly 700changes more steeply than for magnet assembly 300. The positionswitching range for magnet assembly 700 is designated as Q. 300. Theposition switching range for magnet assembly 300 is designated as R. Theposition range R is larger than position range Q. In other words, withnominal tolerances in the switch point of the Hall effect device, magnetassembly 300 will display more variation in switch position than willmagnet assembly 700. The higher flux gradient is due to the polereversal created by magnets 702 and 703.

Clutch Position Sensor and Switch

In accordance with the present invention, a non-contacting clutchposition sensor and switch 800 is shown in FIGS. 7, 8 and 9. Clutchposition sensor and switch 800 includes a housing 810, cover 820, magnetholder 830, magnet assembly 300, circuit board 840, connector shroud850, clutch bracket 900 and clutch pedal 910. Housing 810 has a cavity812, a pedal opening 813, a mounting hole 814 and bearing races 815.Housing 810 can be injected molded plastic.

Magnet holder 830 has bearing holders 832, dovetail portion 833 andmagnet cavity 834. Magnet assembly 300 fits into and is retained bymagnet cavity 834. Magnet holder 830 can be injected molded plastic.Ball bearings 836 are located between bearing holder 832 and bearingraces 815. Magnet holder 830 moves in housing 810 along bearing races815. Printed circuit board 840 holds switch Hall effect device 112 andlinear Hall effect device 114. The Hall effect devices have leads thatare soldered to the printed circuit board. The printed circuit boardholds the Hall effect devices in air gaps 516 and 576. The printedcircuit board has terminals 842 that extend into connector shroud 850.Circuit board 840 is press fit into connector shroud 850. Printedcircuit board 840 can also have signal amplification and conditioningcircuitry mounted on it.

Cover 820 has an aperture 822 through which the printed circuit boardpasses. Seal 826 makes a seal between connector shroud 850 and cover820. Cover 820 is heat staked to housing 810. Clutch pedal arm 910extends through housing opening 813 and is mounted to magnet holder 830.Dovetail portion 833 fits into a corresponding dovetail receptacle (notshown) on pedal arm 910 in order to retain magnet holder 830 to pedalarm 910. Clutch sensor 800 is mounted to clutch bracket 900 by bolt 902through mounting hole 814. A rod 920 extends through pedal arm 910 andbracket 900. Rod 920 rotatably supports pedal arm 910.

When clutch pedal arm 910 is depressed by a vehicle operator, magnetholder 830 and magnet assembly 300 moves with respect to printed circuitboard 840. With Hall devices 112 and 114 fixed in place, theirrespective electrical output signals change in response to the positionof pedal arm 910. As the magnetic field generated by the magnets 300 anddetected by the Hall effect device 114 varies with rotation, the signalproduced by the Hall effect device 114 changes accordingly, allowing theposition of the pedal arm to be ascertained.

While the invention has been taught with specific reference to theseembodiments, someone skilled in the art will recognize that changes canbe made in form and detail without departing from the spirit and thescope of the invention. The described embodiments are to be consideredin all respects only as illustrative and not restrictive. The scope ofthe invention is, therefore, indicated by the appended claims ratherthan by the foregoing description. All changes that come within themeaning and range of equivalency of the claims are to be embraced withintheir scope.

1. A sensor for sensing position of a moveable object, comprising: amagnet attachable to the object, the magnet having a pair of ends and acentral portion, the magnet generating a slowly changing flux field nearthe central portion and a rapidly changing flux field at the ends; afirst magnetic flux sensor positioned about the central portion of themagnet, the first magnetic flux sensor generating an electrical signalindicative of a specific position of the movable object; and a secondmagnetic flux sensor positioned about the first end of the magnet, thesecond magnetic flux sensor generating an electrical signal indicativeof when the movable object has reached a pre-determined location.
 2. Thesensor according to claim 1 wherein, the first and second magnetic fluxsensors are hall effect devices.
 3. A sensor for sensing movement of amovable object, comprising: a) at least one magnet attachable to themovable object, the magnet having a first end, a second end and acentral portion; b) the first and second ends of the magnet having afirst flux density that changes about the ends; c) the central portionof the magnet having a second flux density that changes more slowlyabout the central portion than about the ends of the magnet; d) a firstmagnetic flux sensor positioned about the central portion of the magnet,the first magnetic flux sensor generating a first electrical signalindicative of a specific position of the movable object; and e) a secondmagnetic flux sensor positioned about the first end of the magnet, thesecond magnetic flux sensor generating a second electrical signalindicative of the movable object reaching a pre-determined location. 4.The sensor according to claim 3 wherein, the second magnetic flux sensorfunctions as a first switch.
 5. The sensor according to claim 3 wherein,a third magnetic flux sensor is positioned about the second end.
 6. Thesensor according to claim 5 wherein, the third magnetic flux sensorfunctions as a second switch.
 7. The sensor according to claim 3wherein, the first electrical signal is linear.
 8. The sensor accordingto claim 3 wherein, the second electrical signal is step shaped.